Milo g



(No Model.) v

' M. G. KELLOGG.

MULTIPLE SWITOHBOARD.

No. 592,317. Patented Oct. 26,1897.

VIIIAII 111 Ullniil VIII),

jnvezwviov 5 By 5 a 7 ia ovw'a/R 5 I UNTTED STATES PATE T OFFICE.

MILO G. KELLOGG, OF CHICAGO, ILLINOIS, ASSIGNOR TO THE KEIILOGGSW'ITCIIBOARD AND SUPPLY COMPANY, OF SAME PLACE.

M ULTIPLE SWITCHBOARD.

SPECIFICATION forming part of Letters Patent No. 592,317, dated October26, 1897.

Application filed November 29, 1889. Serial No. 332,020. (No model.)

To all whom it may concern:

Be it known that I, MILO G. KELLOGG, ofChicago,Illinois,temporarilyresidingat Stuttgart,in the Empire ofGermany,have invented certain new and useful Improvements in Multi pleSwitchboards for Telephone-Exch an ges,

of which the following is a full, clear, concise, and exact description,reference being had to the accompanying drawing, forming a part of thisspecification.

My invention relates to a telephone-exchange; and it consists in asystem of switching and testing the lines thereof to determine whetherthey are in use.

In the accompanying drawing, illustrating my invention, the figure showsthe organization of the circuits and apparatus with which I prefer touse my invention, it being understood that my invention may be used invarious organizations referred to hereinafter.

In the figure, A and 13 represent two boards of a multiple-switchboardexchange, to which are connected the lines of two subscribers namely,subscriber No. 1 and subscriber No. 12.

A and B are sections of spring-jacks, to which the telephonelines areconnected. Each spring-jackis composed of an insulatingsupport a, havinga switch-hole Z in its front portion. In this hole Z is supported atestcontact 3', independent of the other contacts of the jack, except bythe circuit connections. In each jack is a pair of contacts 9 and h,normally with the contact 9 resting upon the contact h, the contact 9being connected to that side of the circuit which runs to thesubscribers station. The anvil h is connected to that side of thecircuit which runs to the annunciator. The test-contactsj arepermanently connected to the limb a of each circuit. The circuit ofsubscriber No. 12 shows the normal connections, running from ground at Gthrough the switch-contacts 11 and 10, electrically connected to eachother by the telephone-switch 7 when in its normal position, thence byway of the primary 4 of the induction-coil, through the battery 6 andtransmit ter 3 in parallel, thence through the bells 2 andcall-generator 1, over the limb b of the metallic to central, thence tothe pairs of contacts g and 77., through these contacts in theconnection 6.

jacks of two or more boards, thence through the line-annunciator w tothe test-contacts j in the jacks of the several boards, thence by way ofthe limb a and receiver 8 at the subscribers station to the contact 12of the telephone-switch, normally in contact therewith. Thetelephone-switch is also connected to the receiver 8 through thesecondary 5 of the induction-coil. The contacts 9 short-circuit thecall-generator and bells when the telephone-switch is in its upperposition-that is, when the telephone is switched for use. This switch isthe usual automatic switch. When the telephone is switched for use, thecircuit 13 short-circuits the battery from the line connections, at thesame time closing its circuit with the primary at of the induction-c0il.In all circuits like poles of the battery are connected to like sides ofthe metallic circuit.

At each board is provided one or more sets of operators cordconnections, shown at board A, and atestingcircuit, shown at each board.The operators cord connection consists of two plugs D, composed ofinsulating material 11, upon which two contacts m and o are mounted, thecontacts m connected by the flexible cord connection (I. The contacts 0are connected together by the flexible cord In the circuit 8 is anoperators looping-in switch P, adapted to introduce in circuit therewiththe annunciator p for clearing-out purposes, the operators telephone set1, or the operators calling-generator B, according to whether the leversof the looping-in switch rest upon the contacts (1, r, or s. Thegenerator B is adapted to ring the bells 2 at the subscribers station inthe usual manner. The plugs D are adapted to be inserted in thespring-jacks A and B, the two contacts m and o of the plugs makingelectrical connection with the two contacts j and g of the jacks,respectively, thus making connection with the line-circuit in the usualmanner. These plugs normally rest upon metallic bases D, whichcross-connect the two contacts we and 0 of the plugs, thus clos ing thecircuit of the operators telephone to the calling-line. The test-circuitat each board comprises a telephone t or any other instrument adapted torespond to a current connected on one side to the ground, as at G,

.and branch 13.

and on its other side to a test-plu g T, adapted to be brought intoconnection with atest-contact j of any jack at its board and therebyestablish a circuit for testing.

The operation of this system is as follows: The subscriber operates hiscall-generator 1, sending a current through the bells 2, battery 6, andtransmitter 3 in parallel, primary 4 of the induction-coil, switch-lever7, contact 12, receiver 8, limb a of the metallic circuit, to theannunciator 0c, thence by way of c ontacts h and g and limb I) back tothe generator. This current operates the annunciator,

. giving a signal to the operator at the board at which it is placed.The subscriber removes his telephone from its hook and the operator,

at central makes connection to the line, as shown, at the board A withthe line of subscriber No. 1, supposing that subscriber No. 1 hascalled, her plug lifting the contact 9 from its anvil h. The operatorthen places her looping-in switch upon the contacts g, therebyintroducing her telephone set into the following circuit: from thesubscribers station by way of limb b, contactg, contact 0, flexible-cordcircuit 6, through the operators telephone, thence to the contact 0 ofthe other plug D, metallic base D, contact m, flexibleeord-cireuit cl'tothe contact m of the firstmentioned plug, contact j to limb a of themetallic circuit, thence through receiver 8. the secondary 5 of theinduction-coil to the telephone-switch 7, thence by contact 9 to limb I)again. The subscribers transmittercircuit consists of three parallelbranches, one containing battery 6, another containing the transmitter3, a third containing the primary l of the induction-coil on closedcircuit through the telephone-switch 7, contact 9,

Varying the amount of current flowing through the transmitter branchvaries the current flowing through the primary of the induction-coil.These variations are transmitted to line by the secondary coil 5.

Speaking into the transmitter 3, subscriber No. 1 orders connectionwith, say, No. 12. The operator at board A then applies her test-plug tto the test-contactj of the jack of line No. 12 to ascertain itscondition. Subscribers telephone being on its hook, as shown, atest-circuit is established as follows: from ground at G, test receivinginstrument t, test-plug T, test-contact j, limb a of the metalliccircuit, annunciator w, limb b of the metallic circuit, through contacts9 and h, which are closed to each other normally or when the line is notswitched for use, thence to the subscribers station, bells 2, generator1, subscribers battery 6, primary 4 of the induction-coil, switch-lever7, contacts 10 and 11 to ground at G. The presence of the battery 6 inthis circuit causes a click in the telephone 15, thereby announcing tothe operator that the subscribers telephone is on'its switch and thatthe line is not switched at central. Transmitter 3 is in parallel withthis test-circuit, but its resistance prevents all the current frombeing shunted therefrom. The battery should not be so strong as tooperate the annunciator 10. Upon finding that the line is free theoperator inserts the other connecting-plug D into the switch tested,loops first her callgenerator 13 and then clearing-out annunciator 19into the cord-circuit by means of the looping-in switch and then leavesthe line connected for conversation. Subscriber No. 12 removes histelephone from its switch for use. It now an operator at board B testseither of these lines while thus connected, her test-circuit will beopen at both contacts g and h and 10 and 11, so that her test receivinginstrument has no current to respond to. If the subscriber 12 shouldhang up his telephone and the lines remain otherwise in their connectedcondition, a test-circuit would exist as follows: from the test-contactjof line 12, for example, to which the test-plug is applied, to the limba of the metallic circuit, thence through the receiver 8 and contacts12, 10, and 11 to ground at G. There is no battery in this circuit toactuate the test receiving instrument.

Another test-circuit would exist as follows:

test-contact 7' at board 13, as before, by limb or to the contact j atboard A, contact on of the plug D, circuit 01, to the contact m of theother plug D, contactj of subscriber No. 1, thence by way of limb a,receiver 8, contact 10 of the switch 7, contact 9, limb Z), to central,contacts 9 and o, circuit 6, containing the clearing-out annunciator 19,contacts 0 and g, in connection when plug D is connected with line No.1, limb b of the metallic circuit to the subscribers station, bells 2,generator 1, battery 6, primary coil 4, telephone-switeh 7, contacts 10and 11, to ground at G. If the battery 6 is too strong, it will operate.the test receiving instrument of the operator at board B, causing a freetest when the lines are busy. To obviate this, the battery 6 may be soadjusted as to strength to the test receiving instrument used that withthe added resistance of another circuit the test receiving instrumentwill not respond in the usual manner.

If both lines are connected at central and both telephones are upontheir switches at the subscribers stations, the test receivinginstrument will be short-circuited with reference to the test-batteries,so that the instrument will be practically out of the circuit of eitherbattery when the test is applied. Any closed circuit which contains thetest receiving instrument when the lines are connected together and thetelephones are on the switches and the test is applied may be tracedthus: from the ground at the central office through the test receivinginstrument and test-plug to contact j, to which the plug is applied,thence in either direction to one of the subscribers stations throughhis line conductorato the lever 7 of his telephone-switch, thencethrough the short-circuit connection at that station formed by theconnection of the switch-lever with contact 11 of the switch and thewire to ground. This circuit includes the resistance of the testreceiving instrument, the line conductor, and the subscribers receiver.The circuit containing the testbatteries may be traced from groundthrough the contact 11, the switch-lever 7, thence through thesubscribers battery 6, signal-receiving bell 2, and limb b to thecentral office, thence through the cord conductor 2 to limb b of theother subscribers line to his station, and through his signal'receivingbell and batteryto the lever 7 of his switch, and thence to groundthrough the lever and contact 11 of the switch which is connected to theground. It will be seen that the circuit containing the test-batterieshas two branches from each switch when the lines are tested, one branchbeing over the line conductor a to a contact j and a grounded testoutfit connected thereto, the other branch being through the shortcircuit around this branch from contact 11 to ground. This circuit toground being of practically no resistance and the other circuit toground, that through the test outfit being a long circuit of muchresistance, the circuit which contains the test receiving instrument isshort circuited by this subscribers ground connection of practically noresistance. Again, tracing the circuit back from one subscribers groundthrough the batteries and the two connected limbs I) Z) of the two linesand thence back at the central office to ground through the limb a ofthe second subscribers line and the test receiving instrument, theground connection to the circuit at the second subscribers station beingof prac tically no resistance, and the circuit back to ground throughthe limb a and the test receiving instrument being of considerableresistance, the test receiving instrument is then short-circuited withreference to the batterycircuit.

It is of course understood that my invention maybe used in variousorganizations, in grounded-circuit systems, in law systems, and invarious other organizations well known to the art; nor do I limit myinvention to systems in which switches and plug and cord connections areused, for it is obvious that various other kinds of mechanism andapparatus may be used to accomplish the same functions.

It is also evident that instead of magnetic telephones bells may be usedas test receiving instruments. Certain switching apparatus isunnecessary in such a system suitably modified.

The annunciators of the various lines are distributed among the variousboards to equalize the work of the various operators.

I11 multiple-switchboard systems in which the test receiving instrumentand the testbattery are in a ground connection of the test outfit at thecentral office and in which the test depends upon the ground connectionof the line either at the subscribers station or at central open whileeither the line or the subscribers telephone is switched for con-Versation any accidental ground on the circuit of two lines connectedtogether for conversation will whenever either busy line is testedproduce a false signal that the line is free or not in use. The operatorwho made the test and obtained the false signal will switch the linewith another line, thus connecting the three lines together and producin g confusion. This renders the test system for the time beingpractically inoperative as far as these lines are concerned. Moreover, abreak or escape from the circuit to ground, even although of highresistance, will when the magneto'telephone is used as test receivinginstrument produce the same result. Moreover, with line-circuits ofconsiderable static capacity, particularly when cables are used, andwith magnet0-telepl1ones as test receiving instruments the flow ofcurrent from the battery to the line when the test is made will producethe false signal even though there is no ground or ground escape fromthe circuit of the two connected lines. With the organization hereindescribed with the test-battery, one for each line, located in thecircuit of the line and cut out from the line-circuit while thesubscribers telephone is switched for use no false signal from thebattery can be produced in the test receiving instrument when the testis made, and confusion incident to the other system described above isthereby avoided. This result and advantage is obtained by the positionof the batteries in the circuits for testing, as herein described.

In multipleswitchboard systems an operator to whom certain lines areassigned to answer frequently receives several calls at practically thesame moment, and it may take some time before she can switch to acertain line and answer its call. In systems in p which the test onlydepends upon the switching of the line at some other board anotheroperator may in the meantime test the line, and finding it to test freemay switch it with another line, causing annoyance and confusion to thesubscriber. In my system this trouble is obviated, for as soon as thesubscriber takes his telephone from its switch the line will test busywhether or not it is switched at the central oltice.

Again, in systems of testing which depend only on the subscriberstelephone being oil or on its switch confusion frequently occurs when asubscriber places his telephone on his switch after finishingconversation without sending any clearing-out signal, and his line willtest free and be connected to when it is already switched at the centraloffice. Lines in this condition are technically called tied up. In mysystem again this trouble is obviated because the line will test busyuntil it is disconnected at the central oltice whether or not thesubscribers telephone is on its switch. The system therefore combinesopened when the subscribers telephone is.

switched for use, and including also a testbattery individualto thesubscriber and located in said circuit between said normally closedcontacts at central and at the subscribers station.

2. In a multiple switchboard exchange, a telephone-line, a test-circuitassociated therewith including normally closed switchboardcontacts,opened when said telephone-line is switched for use at central, andincluding normally closed switch-contacts at the subscribers stationopen while the telephone is switched for. use, and including also a tesbattery individual to the subscriber and located in said test-circuitbetween said contacts at central and at the subscribers station switchedfrom said test-circuit while the telephone is switched for use.

3. In a multiple-switchboard exchange, a telephone-line, and atest-circuit, a conductor common to both containing a test-batteryindividual to the subscriber, apair of normally closed switch-contactson one side of said battery, opened while the subscribers telephone isswitched for use, and normally closed switchboard-contacts at central onthe other side of the battery, open while the telephoneline is switchedfor use thereat.

4. In a multiple-switchboard exchange, a telephone-line containing inthe order named a normal ground connection at the subscribers station,telephone switch contacts by which said connection is opened when thetelephone is switched for use, a combined test and transmitter battery,normally closed switchboard-contacts at two or more boards opened whilethe line is switched for use thereat, and test-contacts at said boards,in combination with grounded test receiving instruments at said boardsadapted to be connected to said test-contacts for testing. Y

5. In a multiple-switchboard exchange, a metallic-circuit line andtest-circuit associated therewith containing,in the order named,

a normally closed ground connection at the subscribers station, acombined test and transmitter battery, a line conductor,switchboard-contacts at central normally closed but open while the lineis switched for use, testcontacts at said boards, and a return-conductorconnected at the subscribers station to the normally-grounded limb, incombination with grounded test receiving instruments adapted to beconnected to said test-contacts for testing.

6. In a multiple-switchboard exchange, a telephonedine, atest-circuitassociated therewith including normally closed switchboardcontacts atcentral, opened while in use, and including a pair of normally closedswitchcontacts at the subscribers station opened when the subscriberstelephone is switched for use, and including also a test-batteryindividual to the subscriber and located in said test-circuit betweensaid normally closed contacts at central and at the subscribers station,switched from said circuit while the line is in use.

7. In a multiple-switchboard exchange, a t-elephone-line,atest-circuit,a conductor common to both, containing an individualtestbattery when the subscribers telephone is not switched for use butnot otherwise in said circuit, a pair of normally closed switch-contactson one side of said battery opened While the subscribers telephone isswitched for use, and normallyclosed switchboard-contacts at central onthe other side of said battery open while the line is there switched foruse.

8. In a multiple-switchboard exchange, two tied-up lines connectedtogether at a board, subscribers outfits in their normal position,test-batteries in said lines, grounded test receivinginstruments appliedto said connected lines for testing, and ground connections shortcircuiting said test receiving instruments rendering them unresponsiveto said battery or batteries.

9. In a multiple-switchboard exchange, two tied-up lines connectedtogether at a board, a test-battery in each of said lines, a testreceiving instrument in circuit with said batteries, and a short circuitrendering said instrument unresponsive to said batteries.

In witness whereof I hereunto subscribe my name this 4th day of October,1889.

MILO G. KELLOGG.

\Vitnesses:

MARGARETHA RIEHL, FRANCES D. KELLOGG.

